The unavailability of clean drinking water is one of the significant health issues in modern times. Industrial dyes are one of the dominant chemicals that make water unfit for drinking. Among these dyes, methylene blue (MB) is toxic, carcinogenic, and non-biodegradable and can cause a severe threat to human health and environmental safety. It is usually released in natural water sources, which becomes a health threat to human beings and living organisms. Hence, there is a need to develop an environmentally friendly, efficient technology for removing MB from wastewater. Photodegradation is an advanced oxidation process widely used for MB removal. It has the advantages of complete mineralization of dye into simple and nontoxic species with the potential to decrease the processing cost. This review provides a tutorial basis for the readers working in the dye degradation research area. We not only covered the basic principles of the process but also provided a wide range of previously published work on advanced photocatalytic systems (single-component and multi-component photocatalysts). Our study has focused on critical parameters that can affect the photodegradation rate of MB, such as photocatalyst type and loading, irradiation reaction time, pH of reaction media, initial concentration of dye, radical scavengers and oxidising agents. The photodegradation mechanism, reaction pathways, intermediate products, and final products of MB are also summarized. An overview of the future perspectives to utilize MB at an industrial scale is also provided. This paper identifies strategies for the development of effective MB photodegradation systems.

https://www.mdpi.com/2073-4441/14/2/242/pdf?version=1642404093

Review on Methylene Blue: Its Properties, Uses, Toxicity and Photodegradation

Semiconductor assisted photocatalysis has attracted a pronounced attention owing to its vital role in environmental remediation. Effective light absorption, particularly in the visible region, and charge separation are the two most important factors affecting a photocatalytic system which is generally hard to be achieved by the bare photocatalysts. The blending of various semiconductor materials for the fabrication of heterojunction enhances the photocatalytic activity and stability by decreasing the rate of combination of electron-hole pairs. This review succinctly outlines the recent progress in the synthesis methods and the photocatalytic performances of semiconductor-semiconductor heterojunctions and semiconductor-carbon heterojunctions for degradation of pollutants like dyes, antibiotics, insecticides, herbicides, pesticides, and water splitting. The review ends with a summary and some future perspectives on this fast-emerging area of research.

Photodegradation of organic pollutants using heterojunctions: A review

An environmentally sound approach towards the green synthesis of zinc oxide nanostructures has been achieved with an aqueous extract of Calliandra haematocephala leaves. The nanoparticles were characterized using various analytical techniques to substantiate the structural details. An absorption band at 358 nm corresponds to the formation of zinc oxide nanoparticles. Scanning electron microscopy revealed the nanoflower morphology of the nanoparticles. Energy dispersive spectral analysis portrayed the strong presence of zinc and oxygen, while X-ray diffraction showed the nanoparticles to conform to hexagonally-formed wurtzite structure. The crystallite size of the nanoflowers was estimated to be 19.45 nm. Vibrational frequencies, typical of zinc‑oxygen and other functional groups, were revealed using Fourier transform infrared spectroscopy. BET analysis revealed that the pores were of mesoporous nature with an estimated specific surface area of 9.18 m2/g. The photocatalytic nature of the nanoparticles was established by the degradation of methylene blue (MB) dye, under solar radiation. Up to 88% degradation was achieved in a duration of 270 min. Kinetic data from the studies proved that the reaction was compliant with first-order model, with rate constant as 0.01 min−1. The study illustrated the synthesis of zinc oxide nanoparticles using a novel source, viz., the leaves of C. haematocephala.

Synthesis, characterization and photocatalytic dye degradation capability of Calliandra haematocephala-mediated zinc oxide nanoflowers.

Solar photocatalytic abatement of tetracycline over phosphate oxoanion decorated Bi2WO6/polyimide composites

Zn0.9Ce0.05M0.05O (M = Er, Y, V) nanocrystals: Structural and energy bandgap engineering of ZnO for enhancing photocatalytic and antibacterial activity

Ping Li

Papers

Photocatalytic degradation of methylene blue in aqueous solution by using ZnO-SnO2 nanocomposites

Preparation of ZnO/Bi2WO6 heterostructures with improved photocatalytic performance

Preparation and optical and photocatalytic properties of Ce-doped ZnO microstructures by simple solution method